There’s a question that seems to come up every winter. And every year, since Babfar was founded in 1969, our answer has been the same. Customers ask about using heaters inside an enclosure. (Please visit our blog post Do You Prefer the Fuel Efficiency of a Direct-Fired Heater or the Safety of an Indirect-Fired Heater? What if You Could Have Both? to learn more about the different types of heaters). Customers wonder if fuel efficiency can be improved by re-heating the air inside an enclosure. Sometimes manufacturers also propose this. It makes sense, right? A heater would burn less fuel to re-heat air that’s already inside a building than it would be to heat outside air that’s blown into a building, right? Wrong! What’s worse, re-circulating air increases the amount of moisture in the building and raises carbon monoxide (CO) levels. So, for almost 50 years, Babfar has never recommended using temporary heaters inside an enclosure. Instead, our approach has always been to circulate fresh, hot air through a building.
Positive Pressurization Distributes Heat and Fresh AirPositive pressurization acts like an air curtain that you might find at your local grocery store that prevents cold air from entering the store. Strategically placed openings in a building help distribute heat and forces air that has cooled to exit. Positive pressurization circulates heat and ensures a fresh air change inside a structure. Temporary heaters are often placed indoors if they can’t be used with ductwork. As these units recirculate air inside an enclosure, they create negative pressurization. This means cold air is pulled into the building from doors, stairwells, tarp holes, and other openings. While these units might heat their immediate surroundings, they actually create cold drafts in the rest of the building. Temporary heaters capable of blowing fresh outside air into a building can provide the benefits of positive pressurization. This requires that heaters have a high discharge temperature and cubic feet per minute (CFM) rating to force hot air through ductwork and the entire enclosure.
Fuel Efficiency FallacyThis brings us to the topic of fuel efficiency. For similar-rated British Thermal Unit (BTU) heaters, there are significant differences in heat output, air circulation, and fuel consumption. The table below illustrates how Heater B outperforms both Heater R and Heater O using these criteria. In addition, since Heater R and O are re-circulating heaters, they are like space heaters. So, multiple units will be required to heat the entire building. Of course, this increases fuel consumption.